the nearest point/vertex point of linestring

引用https://github.com/Toblerity/Shapely/issues/190

snorfalorpagus commented on 18 Oct 2014

The point returned is the nearest point on the line to the original point. The nearest point is not necessarily an existing vertex in the LineString, and in this case it isn't.

end = Point(19.125150,72.893218)
np = Point(19.12493833590478, 72.89314854771877)
expected = Point(19.124929, 72.893177)

print end.distance(np) # 0.000222767386696
print end.distance(expected) # 0.000224770994572

If you want to find the nearest vertex you should first convert the LineString to a MultiPoint geometry, then use the nearest_points operation (note the minor floating point error):

from shapely.ops import nearest_points
from shapely.geometry import MultiPoint
mp = MultiPoint(route)
print nearest_points(mp, end)[0] # POINT (19.124929 72.89317699999999)

This query requires calculating the distance between the original point and each vertex in the original linestring. 

直线上距离最近的点，不等于定义时用的vertix

而要得到最近的vertix，关键的思路是把Linestring“退化“成vertix的MultiPoint，退化回"点对点"距离问题，就OK了。